|I'm back to the idea that something was disturbed so check connections as already said. |
Another thing that can sometimes happen is an edge connecter is just minutely moved to a tarnished area. Take out the RAM stick (s) and clean the edge connectors with a pencil eraser then pop the sticks in and out a few times to ensure any oxide is removed from the socket too. Worthwhile doing the same on anything that has edge connectors, such as an addon graphics card, also power and signal connectors for the HD if they are SATA.
Always pop back and let us know the outcome - thanks